Nature as a solution for shoreline protection against coastal risks associated with ongoing sea-level rise

The risks from climate change are ever-growing, especially in more vulnerable and exposed regions such as coastlines. The rise in sea level and increase in the frequency and intensity of climate-induced coastal hazards are threatening the increasing coastal populations. Brazil, with its 8,500 km of coast, is one of the countries most at risk from coastal flooding and erosion. Nature-based solutions have been suggested as climate adaptation strategies with the greatest potential to counteract coastal hazards stemming from sea-level rise and safeguard coastal cities. However, there is still a knowledge gap in the scientific literature on the effectiveness of naturebased solutions, especially at large spatial scales in Central and South America. Here, we assessed the risks from climate-induced hazards of coastal erosion and flooding related to sea-level rise on the Brazilian coast, and the effectiveness of nature-based solutions as climate adaptation strategies. We reveal that nature-based shoreline protection can reduce by 2.5 times the risks to the Brazilian coastline. The loss of existing natural habitats would substantially increase the area and population at risk from these climate-induced hazards. Worrisomely, legal mechanisms to protect these natural habitats are few and being weakened. Only 10% of the coastal natural habitats are within protected areas, and these alone do not ensure coastal protection, as our results indicate that the loss of unprotected natural habitats has about the same risk as the total absence of natural habitats. Our results warn of the severe consequences of the continued loss of natural habitats along the coast. Thus, actions towards the maintenance and protection of coastal habitats are paramount for climate adaptation and to ensure the well-being and livelihoods of coastal populations. Brazil has a central role in demonstrating the benefits of strategies based on nature-based solutions for shoreline protection, favoring their implementation worldwide. We provide both the natural habitat maps and the maps with model results with spatial and numerical information so readers can explore the relations between the natural habitats and coastal risk indexes at a subnational level and foster their use by local stakeholders.